This invention provides a new class of solid solvent viscosity depressants for use in preparing blends with block copolymers such as polyether-polyurethane block copolymers, polyester-polyurethane block copolymers, or other block copolymers described below. The blends are useful as adhesives.
Polymers of all types have proven to be very useful materials in modern society, and many different methods have been developed in order to shape them into useful forms. One of the simplest methods is thermal processing, where a polymer is heated to a temperature at which it flows, is then shaped into its final form by processing machinery, and then is allowed to cool and solidify. This method is widely used because it efficiently uses the polymer material, and generally does not produce large waste streams which must be properly disposed of. However, some materials are difficult to process thermally. The polymer may degrade undesirably at the processing temperature, and yet lowering the processing temperature is not always practical because the polymer viscosity becomes too high for proper processing.
Another method of processing polymers is to make solutions by blending a suitable liquid solvent with the polymer. The solution viscosity is often low enough that the processing can be done at room temperature, although processing of heated solutions is not uncommon. In any case, lower viscosities can be obtained at lower processing temperatures than for the pure polymer, which eliminates problems due to degradation at high processing temperatures. Solvent processing does have many drawbacks, however. The solutions are often made from solvents which are highly flammable and/or present health hazards via inhalation and skin contact. The solvents must be removed and properly disposed of, which is often an involved and expensive process, especially as governmental regulations concerning airborne emissions have become increasingly stringent. Solution processing is usually limited to forming the polymer into thin films.
It is important to reduce a polymer""s melt viscosity in some instances, for example, where a polymer has such a high viscosity that it is difficult to extrude or mold. However, sometimes the viscosity cannot be lowered by increasing the temperature because of decomposition concerns, and the disadvantages of traditional liquid solvents make their use unacceptable.
A more recent method of processing polymers is with the aid of solid solvents. Solid solvents are additives which act as a solvent for a particular polymer above a certain temperature A polymer/additive solution forms in which the melt viscosity of the solution is lower than that of the polymer itself. Thus solid solvents are used where it is desired to lower the melt viscosity and/or processing temperature of the polymer. On the other hand, below that temperature, the solid solvent precipitates out of the polymer and becomes a filler. This eliminates the need for solvent removal that is associated with traditional liquid solvents. Solid solvents are generally low molecular weight crystalline compounds. In operation, a properly functioning solid solvent additive melts at or below the processing temperature, and is soluble such that it reduces the viscosity of the polymer/additive blend to a lower level than that of the base polymer. At use temperature of the final article, the solid solvent functions as a filler, not as a plasticizer. For example, if increased softness or tack are not desired in the final article, the use of a solid solvent avoids exacerbating these undesirable properties in comparison to the base polymer. Solid solvents are different from traditional liquid solvents or lubricants. A traditional liquid solvent adversely affects the mechanical properties of a polymer unless it is removed. A lubricant is not soluble in the base polymer and does not reduce viscosity at low additive levels.
Some classes of solid solvents suitable for homopolymers and random copolymers polymers are known. For example Chung U.S. Pat. No. 5,157,068 teaches that low molecular weight crystalline carboxylic acids and their derivatives act as solid solvents to improve the processibility of vinyl chloride polymers; and in U.S. Pat. No. 4,843,117, Chung teaches that dimethyl sulfone does the same for vinylidene chloride polymers. Buckley, U.S. Pat. No. 4,434,262 teaches an improved melt-processible blend of a polyolefin or polyester in which a solid solvent is present that is N, Nxe2x80x2-bis(p-methoxybenzylidene)-alpha, alphaxe2x80x2-bi-p-toluidine; p-methoxycinnamic acid; N, Nxe2x80x2-bis(4-octyloxybenzylidene)-p-phenylenediamine and lithium stearate. However, none of the solid solvents taught are suitable for block copolymers for one or more of the following reasons: Ineffective viscosity depression, excessive deterioration of physical properties, reactivity with the polymer, and excessive volatility at processing temperatures.
A new class of solid solvents has now been found, which properly function as solid solvents when blended into block copolymers. This new class of solid solvents helps overcome some of the dissadvantages traditionally associated with the thermal processing of block copolymers, and yet has little detrimental affect on physical properties at use temperatures. A particularly useful aspect is when the blend is used as an adhesive and the substrate to which the adhesive is to be applied has pores, cavities, or other surface irregularities. This is because with a lower melt viscosity during the application process, the adhesive can more easily flow into the confined spaces of the substrate material. Examples of processes which benefit from the adhesives made from the blends of this invention include lamination of fabrics and sealing of fabric seams.
It is a purpose of this invention to provide a new class of solid solvents for melt-processible block copolymers, such as polyurethanes, e.g. polyether-polyurethane block copolymers or polyester-polyurethane block copolymers, polyester-polyether block copolymers, polyamide-polyether block copolymers, and polyamide-polyester block copolymers.
It is another purpose to provide a new class of solid solvents for adhesives containing the previously mentioned block copolymers.
It is still another purpose to provide seam tapes containing solid solvents for sealing fabric seams.
It is still another purpose to provide protective fabrics with seams sealed with tape containing the new class of solid solvents in certain polymers. By protective fabric is meant a fabric that protects against the adverse influence of liquids, gases, viruses, or the like.
In one aspect, the compounds that have been found effective as solid solvents for block copolymers have a molecular weight less than 600, contain two functional groups selected from either amide or carbamate groups, and have at least two aromatic rings in the structure. Such solid solvents for block copolymers, hereafter referred to as block-copolymer solid solvents, include adipamides, bisacetamides, biscarbamates, and dibenzamides.
In another aspect, the blockcopolymer solid solvents can be represented by the formula:
Rxe2x80x3-X-Rxe2x80x2-X-Rxe2x80x2xe2x80x3
wherein:
where Rxe2x80x3 and Rxe2x80x2xe2x80x3 can be the same or different and are selected from alkyl of 1-6 carbons or phenyl; each X is the same and is selected from divalent amide or divalent carbamate; Rxe2x80x2 is alkylene of 1-6 carbons, methylene diphenylene or oxydiphenylene. And when Rxe2x80x3 and Rxe2x80x2xe2x80x3 are alkyl, Rxe2x80x2 is oxydiphenylene or methylene diphenylene.
It is understood that the aromatic groups may contain common substituents such as alkyl, halo, or the like, so long as the desired properties of the block copolymer are not significantly reduced.
Block copolymers exhibit an unusual combination of toughness and flexibility which has been attributed to a distinct 2-phase morphology at use temperatures. The molecules of the block copolymer consist of 2 types of structures; a stiff section known as the hard segment, and a flexible section known as the soft segment. The hard segment often has high aromatic ring content, and has either a crystalline melting point or glass transition temperature which is higher than the use temperature. The soft segment is usually more aliphatic in nature, and usually has an amorphous structure with a glass transition temperature lower than the use temperature. Whether or not the block copolymer contains aromatic or aliphatic segments, the hard segment is typically in a crystalline or glassy state, while the soft segment is typically in a rubbery state at use temperature. Because these 2 types of structures are insoluble with each other at use temperature, they are phase separated to form different domains. When melt processing block copolymers, the order of the phase-separated domains is reduced, and they may become mixed to a certain degree. However, complete liquid-type randomization of the molecules is difficult to achieve because of the strong thermodynamic insolubility of the 2 types of intra-molecular structures, and even in the melt, block copolymers often continue to display some inter- and intra-molecular ordering. Specifically, this behavior may be attributed to the comparatively low entropy of solubilization caused by the long lengths of the hard and soft segments. As a result, block copolymers usually have comparatively high melt-processing viscosities compared to homopolymers and randomized copolymers of comparable molecular weight.
Solid solvents have now been found that function exceptionally well in block copolymers when the solid solvent has a specific combination of molecular features; 2 or more aromatic rings, 2 amide or carbamate groups, a certain degree of symmetry, and short molecular length. Such molecules show sharply changing solubility characteristics with changes in temperature. From a thermodynamic point of view, both enthalpy and entropy components can be looked at to see how the molecular features of these block-copolymer solid solvents affect solubility in the block copolymer. The combination of strong hydrogen-bonding functionalities, aromatic rings, and general symmetry of the molecules result in a very strong tendency to form crystalline structures. In fact, it is sometimes necessary to reduce the symmetry of the molecules somewhat so that the crystalline melting point is not too high. In any case, if a melted blend of this invention is cooled to use temperature, the enthalpy of crystallization component for the block-copolymer solid solvent is so strong that that it overcomes decreases in the blend""s entropy, and the block-copolymer solid solvent becomes insoluble and precipitates out of the block copolymer. Now, the case will be examined when the blend is heated above the melting point of the block-copolymer solid solvent and the melting point/glass transition of the hard segment of the block copolymer. It might be noticed that the block-copolymer solid solvents of this invention often structurally resemble the hard segments of many block copolymers. Since the hard segments and soft segments of block copolymers have difficulty solubilizing with one another, even at high temperatures, one might wonder if these solid solvents will actually solubilize with both types of intra-molecular structures, rather than simply favoring solubilization with the hard segment. There is, however, a key difference between these block-copolymer solid solvents and the hard segment, and that is molecular length. As a result, unlike the hard segment, or the soft segment for that matter, these block-copolymer solid solvents have a very high entropy component with respect to solubilization. Since entropy plays an increasing role in solubilization as temperature goes higher, these block-copolymer solid solvents are able to solubilize with both types of block-copolymer segments at processing temperatures. Therefore, these block-copolymer solid solvents help to strongly reduce melt viscosity because, at elevated temperatures, they diminish residual inter- and intra-molecular ordering in the block-copolymer melt by serving as a solubilizing agent for both sections of the block-copolymer molecule.
Additionally, the structures of the block-copolymer solid solvents of this invention result in other highly desirable attributes besides viscosity depression. They have low volatility, which makes them environmentally friendly for processing temperatures of 200xc2x0 C. and higher, and the final article will not suffer long-term shrinkage caused by sublimation or evaporation. Also, these block-copolymer solid solvents are not significantly extracted by liquid solvents which do not also dissolve the base block copolymer.
Preferred block-copolymer solid solvents for block copolymers are: 
The base block copolymer is preferably a polyester-polyether block copolymer, or a polyurethane block copolymer, especially a polyether-polyurethane or polyester-polyurethane. A preferred polyurethane is comprised of units of methylene diphenyldiisocyanate/polyoxytetramethylene glycol/1,4-butanediol.
Whichever block-copolymer solid solvent is used, it must be chosen to begin to melt into the base block copolymer below the processing temperature of the block-copolymer/additive blend employed, and be chosen to precipitate out of the melt at temperatures above the block-copolymer/additive blend""s use temperature.
In one aspect, the invention is a blend of a block-copolymer solid solvent described above and the base block copolymer in which the solid solvent is present in an amount of between 0.2% and 20% by weight, preferably between 0.2% and 5% by weight, and most preferably between 0.5% and 2% by weight of blend.
In other aspects, the blend will be in the form of a sheet or a tape or coating on a substrate, such as a textile. In an especially preferred embodiment, the blend will form a seam tape for sealing fabric seams.
The blend can be used in a number of forms in articles of clothing. By clothing is meant any wearing apparel including shirts, trousers, sweaters, coats, hats socks, shoes, gloves and the like.